Multi-port battery chargers allow a user to charge a number of battery packs without having to regularly extract a charged battery pack and insert a depleted battery pack from, for example, a single port charger. For this and other reasons, multi-port battery chargers may be preferred over single port battery chargers, especially by users that use multiple tools or systems of tools with regularity. Although multi-port battery chargers are advantageous in such instances, multi-port battery chargers have drawbacks, such as size, energy inefficiency, and the potential for short-circuited charging ports.
For example, conventional multi-port battery chargers require a separate power supply for each charging port. Although these battery chargers are capable of charging one or more battery packs, requiring a separate power supply makes the battery charger physically cumbersome. Also, a separate power supply for each charging port reduces the efficiency of the battery charger due to the hardware and power required to operate multiple power supplies.
Also, switching circuits used by conventional multi-port battery chargers use, for example, relays or transistors. These switching circuits are susceptible to malfunction (e.g., a short circuit), which may be a safety concern when the switching circuit is being used to control power distribution (e.g., voltage and current distribution) to an electronic load.
The operation and efficiency of multi-port battery chargers are also hindered by devices and techniques for detecting the presence of a battery pack in one of the charging ports. For example, multi-port battery chargers often use a control circuit that monitors the voltages of a pair of charging port power supply terminals. The charging port power supply terminals are continuously powered, and the power supply voltage must be greater than the voltage of the inserted battery pack for the battery charger to detect and charge the battery pack. When a battery pack is inserted, the voltage at the power supply terminals is reduced, and the control circuit determines that a battery pack has been inserted. However, an empty battery charger (e.g., a battery charger with no battery packs inserted for charging) using this technique for battery pack detection remains in a detection mode for days, weeks, or longer, with the charging port power supply terminals being continuously powered.
Alternatively, a battery charger power supply is operated in a low-voltage state and periodically switches the battery charger power supply to a high-voltage state to provide the voltage necessary to check power terminal voltages and determine if a battery pack is inserted. While periodically switching from a low-voltage state to a high-voltage state to check for the presence of a battery pack uses less energy than the above-described technique, this alternative technique makes the battery charger susceptible to long waiting periods during which the battery charger is constantly checking for the insertion of a battery pack.
Additionally, although snap switches such as those available off-the-shelf have been used to detect the insertion of a battery pack into a battery charger, each snap switch requires multiple wires to connect to a printed circuit board (“PCB”). The additional wires make assembling the multi-port battery chargers difficult, and the wires may become tangled or get pinched. The snap switches are also susceptible to inadvertent depression by a user or object. Inadvertent depression of the snap switch causes the control circuit to determine that a battery pack has been inserted, and also causes an erroneous charging current to be supplied to a charging port.